In recent years, it has become popular to exchange multimedia data such as sound, images and the like, and a search operation is required in order to obtain such multimedia data.
For example, it can be imagined that after receiving sounds such as music played in the real world, images or CM with a mobile terminal and the like, by using a received signal (a target sound signal or a target image signal), the same music, image or CM can be searched for from a very large CM music data base.
Therefore, a search operation is required of a stored sound signal or a stored image signal which is stored in the data base and which is similar to a sound or image signal as a target sound signal or a target image signal that is directly specified.
As a high speed search method for a time-series signal, for example, Japanese patent No. 3065314 is disclosed. It should be noted that the search operated here is a time-series search that needs to be operated at high speed and accurately.
However, it is believed that the sounds or the images recorded and obtained by a user in the real world include a variety of characteristic distortions, for example, a multiplicative distortion because of characteristics of the apparatus which is a signal source such as a speaker or a screen or because of a characteristic of the mobile terminal, and an additive noise because of elements in the real world (if a sound, it may be noise, echo or absorption, and if an image, it may be clearness of air, haze because of brightness and angle, reflection and so on). In respect to this point, a method in accordance with Japanese patent No. 3065314 makes an assumption such that the signal of a search target has less characteristic distortion, and therefore, if noises or distortions are included, search accuracy is reduced greatly.
In order to solve this problem, a method, by providing a fluctuation appending step in which a fluctuation is appended to an input signal, is proposed which detects signals accurately in respect to the characteristic distortion (for example, see Japanese Patent No. 3408800). However, there is another problem in that upon providing the fluctuation appending step as described above, if multiple noises or distortions are to be considered, multiple target features need to be prepared for these, therefore, the amount of information increases.
A method is proposed in which after detecting the peak level of the input target signal of the sounds or the images, by applying a frequency at the peak level, a signal detection is performed accurately in respect to the noises and the distortions.
However, this method has a problem in that it fails to detect the peak level of the actual signal and the accuracy of searching is decreased because it uses the peak level of the input signal and it is influenced by high noise level around the peak level of the actual signal.
Therefore, a method of signal detection is desired with high accuracy against distortions by normalizing the input target signals of sounds or images using the statistics of local feature. In other words, in this signal detection method, in order to reduce the fluctuations of the target signals of the sounds or the images because of the characteristic distortions, after extracting the frequency characteristics, a data conversion to a coordinate system with high accuracy against distortions is performed by normalizing the target signals at every local area on a time-frequency coordinate system, and based on this coordinate system a comparison between the sounds or the images and the stored data is made.
However, the data conversion method to the coordinate system with high accuracy against characteristic distortions described above cannot reduce the characteristic distortions enough upon noise, interruptions or accidental distortions by using only the normalization, therefore, it has a problem in that the reliability of searching is decreased.
The present invention was devised in light of the above problems, and has as an object of developing the search accuracy by converting the sound signals or image signals to be searched for (target signal: target sound signal and target image signal) to data with high accuracy against the additive noise or interruptions, and of reducing searching time greatly.
The present invention has as an object of developing the search accuracy by converting the signals including the multiplicative distortions to data with high accuracy, and of providing a system which can execute a process with high speed and high accuracy.
The present invention has as an object of providing a signal search apparatus, a signal search method and a signal search program and medium which can develop overall search accuracy by applying a method of quantization that increases reliability of values after quantization rather than before linear quantization.